Distribution of IgG4- and/or IgG-Positive Plasma Cells in Hashimotos Thyroiditis: An Immunohistochemical Study

Background and Study Aim: Recently, immunohistochemistry has shown numerous IgG4-positive plasma cells in a subset of Hashimoto’s thyroiditis (HT), and this type of HT (IgG4 HT) appears to be a subtype of IgG4-related sclerosing disease. However, little is known about the distribution pattern of plasma cells in IgG4 thyroiditis. To clarify the distribution pattern of IgG4-positive plasma cells, 33 cases of HT demonstrating abundant lymphoplasmacytic infiltrate were studied. Methods: Using formalin-fixed paraffin-embedded sections, histological, immunohistochemistry and polymerase chain reaction were performed. Results: Fourteen cases were classified as IgG4 HT and 19 cases were non-IgG4 HT. Histologically, there was no significant difference between the 2 groups with regard to the degree of stromal fibrosis, lymphoid follicle formation, or the presence of phlebitis or fibrous thyroiditis. The present study demonstrated 2 distribution patterns of IgG4and/or IgG-positive plasma cells, namely the interfollicular (n = 31) and intrafollicular + interfollicular patterns (n = 2). Interfollicular plasma cells Received: June 16, 2010 Accepted after revision: July 26, 2010 Masaru Kojima, MD Anatomic and Diagnostic Pathology, Dokkyo University School of Medicine 321-0293 Mibu (Japan) Tel. +81 282 86 1111, ext. 2178, Fax +81 282 86 5171 E-Mail k-masaru @ dokkyomed.ac.jp © 2010 S. Karger AG, Basel 1015–2008/10/0775–0267$26.00/0 Accessible online at: www.karger.com/pat M.K. and M. H. contributed equally to this work. D ow nl oa de d by : 54 .7 0. 40 .1 1 11 /2 3/ 20 17 2 :4 5: 10 A M Kojima /Hirokawa /Kuma /Nishihara / Masawa /Nakamura /Miyauchi Pathobiology 2010;77:267–272 268 lymph nodes as well as elevated serum IgG4 level, and shows a good response to steroid therapy [2, 3] . It is characterized by prominent lymphoplasmacytic infiltration and sclerosis as well as numerous IgG4-positive plasma cell infiltrations [3] . The fibrous variant of HT is characterized by a marked fibrous replacement of one third or more of the thyroid parenchyma [4, 5] . Harach and Williams [6] found that the fibrous variant of HT contained numerous IgG-positive plasma cells. In 2005, Komatsu et al. [7] demonstrated a high prevalence of hypothyroidism among patients with autoimmune pancreatitis. Histopathological and immunohistochemical findings of the fibrous variant of HT are similar to those of IgG4-related disease. Recently, Li et al. [8, 9] demonstrated that from both clinical and histopathological [i.e. presence of prominent fibrosis, numerous IgG4-positive plasma cells and elevated serum IgG4 level ( 1 135 mg/dl)] perspectives, IgG4 HT and non-IgG4 HT appear as distinct entities [3] . They emphasized that measuring the serum IgG4 level provided a useful method of distinguishing IgG4 HT from non-IgG4 HT [9] . In IgG4-related lymphadenopathy, Sato et al. [10] classified two types of IgG4-related lymphadenopathy by the infiltration pattern of IgG4positive plasma cells: interfollicular plasmacytosis and intragerminal center plasmacytosis. However, little is known about the distribution pattern of IgG4-positive plasma cells in IgG4 HT. To clarify the presence or absence of 2 types of IgG4-positive plasma cell infiltration in IgG4 HT, we studied 33 cases of HT demonstrating prominent lymphoplasmacytic infiltration in comparison with non-IgG4 HT. Patients and Methods Thirty-three patients with HT who underwent total thyroidectomy at Kuma Hospital (Kobe, Japan) between 1983 and 2006 were reviewed. According to the Guidelines of the Japanese Thyroid Society, all patients were diagnosed as having HT based on clinical findings: diffuse swelling of the thyroid gland without any other cause (such as Graves’ disease) accompanied by any one of the following laboratory findings: (1) positive for antithyroid microsomal antibody or antithyroid peroxidase antibody, (2) positive for antithyroglobulin antibody, and (3) lymphocytic infiltration in the thyroid gland confirmed with cytological examination. Incidental findings of focal (nonspecific) lymphocytic thyroiditis in tumor-bearing thyroid tissue were excluded from this study. This study was approved by the Kuma Hospital Bioethical Committee. Surgical specimens were fixed in formalin, routinely processed and embedded in paraffin. For light-microscopic examination, the sections were stained with hematoxylin-eosin (HE) and Victoria blue-HE stain. Immunohistochemical studies were performed using automated Histofine Histostainer (Nichirei Bioscience Inc., Tokyo, Japan) according to the manufacturer’s instructions. The panel of antibodies included human immunoglobulin light chains (kappa and lambda; Dako A/S, Glostrup, Denmark), IgA (Dako), IgG (Dako), MCO011 (IgG4; Binding Site, Birmingham, UK), IgM (Dako) and a cocktail of 2G9 (CD21; Novocastra) and RB L25 (CD35; Novocastra). If necessary, polyclonal CD3 (Dako), 56C6 L26 (CD20; Dako), DFT-1 (CD43; Dako), 124 (bcl-2; Dako), AE1/3 (cytokeratin; Dako) and antithyroglobulin antibody (Dako) were also stained. Sections with known reactivity for the antibodies assayed served as positive controls and sections treated with normal rabbit and mouse serum served as negative controls. In selected cases, genomic DNA was extracted from formalinfixed tissues after dewaxing of paraffin sections; then immunoglobulin heavy chain (IgH) rearrangement was analyzed by polymerase chain reaction as described previously [11] . IgG4 HT was defined by the criteria of Li et al. [8, 9] , i.e. (1) greater than 20 IgG4-positive plasma cells/high power field and (2) greater than 30% IgG4/IgG ratio. The degree of stromal fibrosis and lymphoid follicle formation was examined and expressed as 3+ = severe, 2+ = moderate, and 1+ = mild. Comparison of frequency data between the 2 groups was performed using the Fisher exact test. For continuous data, intergroup comparisons were performed using the Mann-Whitney U test.